1. Field of the Invention
The present invention relates to a reference current generator in a semiconductor integrated circuit for generating a reference current such as a current substantially proportional to absolute temperature (PTAT).
2. Description of the Background Art
U.S. Pat. Nos. 5,646,518 to Lakshmikumar et al., and 6,150,872 to McNeill et al., disclose a PTAT current source that generates a reference current to be used in a semiconductor integrated circuit. The PTAT current source generates a current which increases substantially in proportion to absolute temperature, i.e. a PTAT current.
In such a current source, for example, a current varies due to the variability of device parameters caused by the manufacturing process of a semiconductor integrated circuit. To eliminate this problem, for instance, Japanese patent laid-open publication No. 121694/1999 teaches a reference voltage generator including adjusting means for adjusting the level of current in a current source after manufactured in the form of semiconductor integrated circuit. The adjusting means fine-tunes a reference current by utilizing, e.g. fuses and resistance elements, to change the values of resistance.
The conventional adjusting method, however, has a problem that the resistance of switches, when conductive, are incorporated into the resistances. Moreover, in order to improve the adjustment precision, a required number of resistance elements must be provided, which are interconnected to the respective switches having the resistance value thereof slightly different from each other. It leads to an increase in size of the circuitry.